Why do some grasses stop growing and change colour during winter?
There are two different families of lawn: warm-season grasses and cool-season grasses. As their names suggest, they grow at different temperatures. Warm-season varieties such as Sir Walter DNA Certified Buffalo, Eureka Premium VG Kikuyu, Sir Grange Zoysia, and TifTuf Bermuda generally slow down during the cooler months, especially in southern areas of Australia like Victoria. We call this slowing of growth dormancy.
Different grasses go into different levels of dormancy depending on their composition and the ambient temperature. Dormancy allows the grass to minimise metabolic activity, helping it to conserve energy. Once soil temperatures drop below 14 degrees in Victoria, usually starting in May, warm-season grasses will start to slow down to protect themselves from the harsh conditions of winter.
In Melbourne, the cool season is much more limited than, for example, in many parts of North America and Europe. This is part of the reason why warm-season varieties are so much more common than cool-season varieties such as fescue, rye, and bentgrass. Because the cool season is so limited, some warm-season varieties never really go fully dormant and continue to grow throughout winter – just at a much slower rate.
During winter, you may go from mowing your lawn weekly to only fortnightly, or for a while you may even get away with not mowing at all. Dormancy is more common in Melbourne than in the more northern cities such as Brisbane and Cairns, where lawns tend to grow fairly actively all year round.
During dormancy the colder temperatures and frost damage may cause the colour of your lawn to lighten. The degree of discoloration and damage caused by frosts depends largely on the variety you have. Cool-season grasses such as fescue and rye contain proteins that prevent them from freezing; warm-season grasses don’t have this protein so are much more susceptible to these frosts.
What can you do to help your lawn tolerate frost?
Use a fertiliser with increased iron before winter to enhance frost tolerance.
Whenever there is frost on the lawn, stay off it. Walking across it can cause the blades to break, worsening the damage.
Give your lawn a very light watering just before the sun comes up in the morning to melt the frost more quickly and evenly and reduce the chance of brown patches.
Just as tree leaves change colour to beautiful golden browns and oranges in autumn, warm-season grasses can vary in colour throughout the year depending on growth and temperature, and this is nothing to worry about. You can fight it, but it is easier to embrace it and enjoy the variation.